Synthesis of semiconducting β-FeSi2 bulk material often involves prolonged annealing to eliminate the intermediate ε-FeSi phase. This inevitably results in severe grain coarsening, degrading thermoelectric properties. Our approach is based on the eutectoid transformation α-FeSi2 → β-FeSi2 + Si. By mixing cast α with Ge via ball milling, we find that the Si product phase alloys with Ge during spark plasma sintering. A well-sintered β-FeSi2/Si1-xGex nanocomposite with consistent composition has been obtained at temperatures below 900℃ in just a few minutes, with no post-annealing. Its hierarchical structure is promising for reducing lattice thermal conductivity. We achieved facile tuning of the Ge concentration in the diamond cubic phase, which should enable engineering of the band structure across the heterointerfaces to enhance electrical transport. In addition, modulation doping may be achieved by preferentially doping β-FeSi2, taking advantage of the high mobility of undoped SiGe. Support by the II-VI Foundation is gratefully acknowledged.